[clang] clang/AMDGPU: Set amdgpu-max-num-workgroups to disable Y/Z by default (PR #119009)

[Shilei Tian via cfe-commits]

shiltian wrote:

> So this is wrong. It was correct for openmp.

Even OpenMP is discussing to introduce multi-dim support, though in LLVM I already implemented it as an extension. :-)

https://github.com/llvm/llvm-project/pull/119009